Abrasive articles and methods of making the same



Aug. 7, 1962 E. HURST 3,043,482

ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Filed Oct. 22, 1958 2 Sheets-Sheet 1 FIG. 2

FIG.3 22

A u INVENTOR.

E DWAR D HURST ATTONEY Aug. 7, 1962 E. HURST 3,048,482

ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Filed Oct. 22, 1958 2 Sheets-Sheet 2 FIG.8

INVENTOR. EDWARD HURST 3,048,482 ABRASIVE ARTICLES AND METHODS OF MAKING THE SAME Edward Hurst, Duxbury, Mass, assignor to Rexali Drug C0., Los Angeles, Calif., a corporation of Delaware Filed Oct. 22, 1958, Ser. No. 769,010 4 Claims. (Cl. 51-298) This invention relates to the manufacture of abrasive products. More particularly, it pertains to a novel type of abrasive article, in the form of a disc, belt, wheel or other configuration and comprising a flexible support or backing to which is secured an abrading body made up of a multiplicity of individual small abrasive bodies which function separately and collectively in conjunction with a retaining matrix as the abrading component of the article. According to a modification of the invention, one or more plies of the matrix material containing the individual small abrasive bodies is secured as a facing to one or both lateral faces of a flexible or rigid bonded abrasive wheel or disc. The invention also embodies methods for making such products.

There has been a long-standing and insistent demand and need for abrasive products embodying certain specific, highly desirable qualities. The primary qualities are listed as follows:

(1) Free-cutting abrasive action.

(2) Controlled flexibility.

(3) Multiple grain thickness of abrading component.

(4) High strength with accompanying high speed safety factor.

(5) Resilient or cushioned action comparable to the effect of a built-in shock absorbing media.

(6) Controlled intermittent cutting action similar to saw-tooth cutting action.

(7) Thorough and effective utilization of the abrasive material.

(8) Extraordinarily long life of the abrasive product.

The prior art has offered many different forms of abrasive products, each of which has provided one or more of these qualities to some degree but always at a sacrifice of one or more of the other equally desirable qualities or features. For example, a conventional coated abrasive belt or disc has a high degree of flexibility and free-cutting action but is of inordinately short life because of the limitation of the abrasive coating to substantially a single grit size in thickness. Again, ordinary rigid bonded grinding wheels, although stronger and of much longer life than conventional coated abrasive products, lack the flexibility and much of the versatility offered by the latter type of product. Efforts heretofore to provide a single article offering these various characteristics or qualities have met with little or no success.

It is therefore an object of the present invention to provide an abrasive product that can be made in flexible form such as in the form of a belt, disc or other shape, but is not restricted to a single layer of abrasive grains substantially one grit size thick and which will have much longer life.

It is a further object to provide abrasive articles of highly efficient cutting action over prolonged periods of time.

It is a still further object to provide abrasive articles of many different forms in which the abrasive is effectively and efficiently used without sacrifice of durability and strength.

It is still another object to provide practical and economical methods for making abrasive articles of the aforesaid described type.

Other objects and advantages accruing from the pres-.

nitcd ttes atom:

ice

ent invention will become obvious as the description of the invention proceeds.

The present invention is based on the mechanical concept of fabricating an abrasive article of a predetermined number of individual small strongly or rigidly bonded abrasive bodies, appropriately designated herein as abrasive micro segments or micro segmental bodies, each of these small abrasive bodies positionized into a pattern for effective abrading and yet yieldably supported so as to have a controlled mobility whereby fresh cutting facets of the abrasive micro segments are constantly presented at the abrading face of the article. Furthermore, the resulting abrasive article is of over-all flexible character, unless specifically designed to be otherwise, despite the fact that the abrading component is of substantial thickness. I have accomplished these objectives by forming an abrasive article from a multiplicity of individual rigidly bonded abrasive bodies mounted or supported in a surrounding resilient matrix or reticulum in such a way that the rigid abrasive bodies can be described as being hinged to the ribs of the reticulum. The reticulum is also abrasive in character, and preferably reinforced by a network of filamentary material, the resulting abrasive component made up of the abrasive bodies and surrounding reticulum being suitably mounted or secured upon a backing or support to form the desired article, such as an abrasive belt or disc, grinding wheel, set-up wheel, polishing wheel or other shape. According to another modification of the invention, the abrasive reticulum bearing the positionized micro segments is applied to one or both lateral faces of a grinding wheel, such as a cutting off wheel, or to the one side of a depressed center disc wheel, to impart an abrasive surface of patterned roughness.

In order that the invention may be more clearly understood, reference is made to the various figures of the drawing, in which FIGURE 1 is a top plan view of an abrasive disc made in accordance with the present invention;

FIGURE 2 is a cross sectional view through the line 22 of FIGURE 1;

FIGURE 3 is a view similar to that of FIGURE 2 showing a modified form of flexible abrasive disc made in accordance with the present invention;

FIGURE 4 is a highly enlarged fragmentary cross-sectional view of the annular portion of the abrasive disc of FIGURE 3;

FIGURE 5 is a bottom plan view of one form of reticulum used in making abrasive articles in accordance with the present invention, the view showing the reticulum as filled with the micro segmental abrasive bodies;

FIGURE 6 is a sectional view through a fragment of FIGURE 5;

FIGURE 7 is a perspective view of an abrasive belt made according to the present invention, and

FIGURE 8 is an enlarged sectional view of an abrasive cutting-off wheel embodying certain features of the present invention.

The abrasive articles of the present invention, irrespective of the specific form in which they are made, can be briefly described as consisting of three essential components, namely, (a) a plurality of permanently rigidly bonded small abnasive bodies herein designated as abrasive micro segments or micro segmental abrasive bodies, ([2) a flexible, resilient abrasive-bearing means or reticulum, preferably provided with filamentary reinforcing elements, for retaining the small abrasive micro segments in position for effective cutting action and providing them with a resilient cushioned supporting medium as Well as supplementing their abrasive action, and also serving as a means for mounting or attaching the abrading component to the backing, and (c) a suitable support or backing for. the abrasive micro segments and their cushioned support.

The abrasive micro segments are composed of abrasive grains of any desired grit or particle size or sizes and a heat-hardened, permanently rigid, organic bond such as a heat-hardened phenol formaldehyde resinous condensation product or a vulcanized hard rubber, together with other auxiliary ingredients such as catalysts, vulcanizers, accelerators, fillers or the like to obtain the desired catalytic action, accompanied by vulcanization and/or polymerization under the proper selected conditions of time, temperature and pressure. Suitable compositions for making resin-bonded and rubber-bonded abrasive bodies are too well known to require detailed formulation and description herein, having been disclosed in numerous prior art patents and in the literature. For example the following patents disclose compositions for making resinbonded abrasive bodies suitable for use in carrying out the present invention:

US. Patent No. 1,626,246 to Martin US. Patent No. 2,010,873 to et al.

U.S. Patent No. 2,076,517 and U.S. Patent No. 2,201,321 to Robie and US. Patent No. 2,171,635 to Robie et al.

Similarly, US. Patent No. 1,953,984 to Martin discloses compositions that can be used to make rubberbonded abrasive bodies. Having prepared a distributable mass of abrasive grains and organic resinous or rubber heat-hardenable bond of the selected composition, the individual small abrasive bodies or micro segments are formed and positioned in the supporting matrix or reticulum in the manner described later herein. As pointed out below, the individual abrasive micro segments are preferably given a tapered conformation such as that of a four-sided pyramid in order to provide additional means for securing them against dislodgement during use of the abrasive article.

An abrasivebearing matrix or reticulum that has been found satisfactory as the carrier means and supporting medium for the individual abrasive micro segments described above can be made as follows. Using the process described in Hurst US. Patent No. 2,284,739 an abrasiveincluded fibrous web is formed embodying a permanently thermoplastic resinous polymerization product as the interstitial bonding medium for the interlocked textile fibers and abrasive granules. It is essential for purposes of the present invention that the bonding constituent of the fibrous web he of permanently tough resilient character.

I have found that the thermoplastic resinous polymers, copolymers and heteropolymers of acrylic acids, such as the low and high acrylic esters of acrylic and nrethac-rylic acids are highly satisfactory as the thermoplastic resinous binder of the reticulum or matrix. Among those acrylic polymers which can be used are polymerized methyl acrylate, ethyl acrylate, methyl methaorylate, polymerized metlracrylic acid, butyl methacrylates, propyl methacrylates, both polymerized and copolymerized with one another. Furthermore, any degree of flexibility and toughness in the thermoplastic resinous matrix can be obtained by blends of the various acrylic or iacrylate polymers, or by the use of various plasticizers with the basic polymer. These acrylic resins are compatible with most classes of plasticizers including phthalates, tartrates, phosphates, adipates and the like. The general physical properties of various acrylic resinous materials and how they can be varied by the selection of the correct ester or blend of esters, with or without plasticizers or other modifiers are fully set forth in the literature and in many issued patents.

While I have pointed out above how various acrylic polymers of suitable toughness and flexibility can be used as the binder of the matrix or reticulum for securing the abrasive micro segments together in articles made according to the present invention, other thermoplastic resinous materials comparable to the acrylic resins in these properties can be similarly )llSGd.

After the abrasive-containing fibrous web of fibers bonded by interstitial. thermoplastic material has been A formed, it is subjected to a molding operation, such as by passing it through a set of configurated rollers or subjecting it to pressure between mold plates of suitable design to form in the material a multiplicity of small cavities or pockets, preferably of tapered configuration, extending in from one side of the fibrous web 'or sheet. When the abrasive-included fibrous sheet of thermoplastic material is reinforced with a network of filamentary strands such as nylon or glass fiber strands, the molding operaiton is carried out so that the pockets or cavities formed in the material are in register with the interstices formed by the network of reinforcing filaments. During the formation of the abrasive-included fibrous sheet material a reinforcing network of filamentary strands of nylon, glass yarn or other reinforcements is incorporated into the structure. The molded sheet material is then cut into the desired size and shape for making abrasive articles of the selected form and type. For example, if abrasive discs are to be made the sheet material is cut or died out in the form of discs of a diameter equal to the diameter of the abrasive disc to be made.

After the abrasive grain-resin bond composition has been prepared in sufficient quantity, and the molded abrasive-bearing thermoplastic resin sheet material has been fabricated and cut to size, the abrasive article is assembled and formed as follows. A layer of the molded thermoplastic resinous sheet material is placed upon the bottom plate of a mold with the cavities of the molded sheet material facing upwardly. The abrasive grain-resin bond composition is then placed upon the sheet material and distributed thereover to fill each of the individual patternized cavities thereof. The flexible backing material, cut to the same size and shape as the molded abrasivecontaining reticulum, is placed over the abrasive filled thermoplastic matrix or reticulum, the top mold plate placed over the assembled materials and the entire assembly subjected to heat and pressure for a suflicient period of time to polymerize or vulcanize the resin or other organic bond of the abrasive segments, mature the thermoplastic resin of the reticulum and combine the backing and the abrasive-filled reticulum and form the resultant abrasive article.

Any suitable flexible material can be used as the backing such as one or more layers of latex-filled fabric, canvas, drills, or other suitable flexible materials, the fibers of any of said fabrics being any material or synthetic, organic or inorganic textile fibrous material, such as and including glass or ceramic fibers, nylon or other poly amide fibers, polyester fibers, regenerated cellulose (rayon) fibers and the like, singly or in blends.

Referring further to the drawing, FIGURES l and 2 illustrate an abrasive disc made in accordance with the teachings of the present invention. The flexible disc 10 as shown is 7" in diameter with a 1" central mounting arbor 11. The disc comprises an abrasive layer 12 of substantial thickness bonded to a flexible backing con sisting of two layers 13 and 14- of latex-impregnated burlap or Osnaburg cloth. The abrading component 12 of the disc is constructed of an abrasive-bearing thermoplastic resilient fibrous cushioning matrix 15 provided with a multiplicity of small cavities 16 filled with micro segments 17 of resin bonded abrasive material. The abrasive micro segments 17 are tapered on four sides and are generally pyramidal in shape with the base of the pyramids adjacent the flexible backing of the disc and the tips 18 extending through the fibrous matrix or reticulum 15. The abrasive surface of the disc, as shown in FIGURE 1, consists of a multiplicity of small rigid bonded abrasive bodies constituting the tips or uppermost portions of the individual abrasive micro segments 17 surrounded by the thermoplastic, abrasive containing matrix or reticulum 15. The result is the provision of an abrasive article having a functional surface made up of a multiplicity of isolated small hard-bonded abrasive bodies surrounded and supported by a matrix or zone of softer, more resilient or yieldable material that is also abrasive in character.-

FIGURES 3 and 4 show a modified form of abrasive disc, similar to that shown in FIGURES l and 2, but in which, in addition to the two layers of latex-impregnated fabric 20 and 21 and the primary abrasive layer 22 containing the abrasive micro segments 23 extending over the entire surface of the disc, there is provided a supplementary layer of fabric between the abrasive layer 22 and the uppermost layer 21 of the flexible backing. This secondary layer 24 is of heavy drill cloth in which the annular zone extending in a short distance from the periphery of the disc is molded to form a number of pockets or cavities similar to those provided in the abrasive reticulum of the disc, the cavities being filled with abrasive micro segments similar to those of the primary abrasive layer 22 of the disc. This supplementary layer of abrasive micro segments about the periphery of the disc serves to extend the life of the disc by replacing the layer 22 as it becomes worn away.

FIGURES 5 and 6 depict the preferred type of filamentary reinforced thermoplastic matrix or reticulum in which a network of reinforcing yarns 27 is incorporated within the abrasive-charged fibrous thermoplastic resin reticulum at the time of its fabrication. It can be seen from the structural details of FIGURE 6 how the tapered sides of the micro segments 17 are held by the reinforcing filaments 27 against disruption in the course of grinding. The resilient cushioning action of the matrix or reticulum 15 permits of a controlled mobility of the individual segments 17 and at the same time the abrasive particles 28 contained in the matrix 15 retard the wearing away of the matrix or reticulum prematurely so that as a result the overall cutting action of the disc is rendered effective by reason of the saw-tooth cutting action stemming from the rigidly bonded individual abrasive bodies in conjunction with the abrasive action of the matrix.

FIGURE 7 depicts an endless abrasive belt 30 embodying the same structural features as the abrasive disc shown in FIGURES 1 and 2.

FIGURE 8 shows a resin-bonded cutting-off wheel comprising a resin-bonded abrasive body 31 having bonded to each of the lateral faces a single ply or layer 32. Each of the layers 32 is made up of an abrasivecontaining fibrous thermoplastic resinous reticulum 33 containing a pattern of abrasive micro-segments 34. As a result the sides of the cutting-off wheel are provided in use with a roughened and patterned cutting face in 6 which the abrasive is present in the outermost facets of the roughened surface.

Any of the abrasive materials in common use may be employed in practicing the present invention. Such materials include silicon carbide, fused aluminum oxide grains, flint, natural corundum, emery, rouge and similar substances. The size of the abrasive may vary from the finest polishing or buffing powders to the coarser grit sizes used in grinding.

Having described the invention in detail it is desired to claim:

I. An abrasive article consisting essentially of a multiplicity of small, individual bonded abrasive bodies, each of said bodies being roughly pyramidal in shape and composed of discrete abrasive granules and a rigid heathardened organic bond selected from the group consisting of heat-hardened phenolic resins and vulcanized hard rubbers, each of said small bonded abrasive bodies being held within a cavity conforming in shape to the small bonded abrasive body, the cavities for said bonded abrasive shapes being provided in a permanently flexible matrix composed of a fibrous material containing individual abrasive particles disposed throughout the fibrous material and a permanently resilient, thermoplastic resin bond.

2. An abrasive article according to claim 1 in which the thermoplastic fibrous matrix is reinforced by a network of filamentary strands extending between the abrasive-filled cavities thereof.

3. An abrasive article according to claim 1 in which said article constitutes the facing on the lateral sides of a rigid-bonded abrasive wheel.

4. An abrasive article according to claim 1 in which said article is provided with a flexible fibrous backing adhesively bonded to one side of said flexible matrix as a support therefor.

References Cited in the file of this patent UNITED STATES PATENTS 2,076,846 Johanson Apr. 13, 1937 2,194,472 Jackson Mar. 26, 1940 2,250,119 Williamson July 22, 1941 2,277,520 Martin Mar. 24, 1942 2,292,261 Albertson Aug. 4, 1942 2,952,951 Simpson Sept. 30, 1960 

1. AN ABRASIVE ARTICLE CONSISTING ESSENTIALLY OF A MULTIPLICITY OF SMALL, INDIVIDUAL BONDED ABRASIVE BODIES, EACH OF SAID BODIES BEING ROUGHLY PYRAMIDAL IN SHAPE AND COMPOSED OF DISCRETE ABRASIVE GRANULES AND A RIGID HEATHARDENED ORGANIC BOND SELECTED FROM THE GROUP CONSISTING OF HEAT-HARDENED PHENOLIC RESINS AND VULCANIZED HARD RUBBERS, EACH OF SAID SMALL BONDED ABRISIVE BODIES BEING HELD WITHIN A CAVITY CONFORMING IN SHAPE TO THE SMALL BONDED ABRASIVE BODY, THE CAVITIES FRO SAID BONDED ABRASIVE SHAPES BEING PROVIDED IN A PERMANENTLY FLEXIBLE MATRIX COMPOSED OF A FIBROUS MATERIAL CONTAINING INDIVIDUAL ABRASIVE PARTICLES DISPOSED THROUGHOUT THE FIRBROUS MATERIAL A PERMANENTLY RESILIENT, THERMOPLASTIC RESIN BOND. 